Dear Avijit,

welcome,

In order to be able to recover the sound again after converting it to digital form you have to consider:

the aliasing problem by passing your signal into antialliasing filter which limits the bandwidth of the sound signal to the highest desired one such that one preserves the bulk of the signal and cuts its tail.

Then you have to sample this signal with at least fs>= 2 the maximum frequency contained in the signal. As fs increases the reconstruction of the signal becomes easier but it needs higher speed converters.

Then after sampling you have to convert it into digital form using an A/D converter with the a conversion speed grater than or equal to the sampling frequency.

After that to recover the signal again you have to use the appropriate speed and resolution. Then you pass the signal into low pass filter to extract the original signal from the back converted waveform.

You can use also interpolation after backconvertion.

Best wishes

Thanks Abdelhalim Zekry sir. But can you please provide me some examples which can be helpful.

Welcome again dear Avijit,

What sound do you have? do you have speech? Then you normally limit your bandwidth to 3.4 KHz , and use a sampling frequency of 8 kHz, an A/D converter with a resolution of 12 bit signed folded code. It can be compressed by A or u law to 8 bit per sample. This if you want to transmit or store it. The speed of the A/D converter must be greater than 8 ksamples/second. In the receiver to restore the signal you must perform the reverse opearions of decompression, D/A conversion and interpolation.

Best wishes

Dear Avijit,

welcome,

To make a sound to the binary form, you have to quantify the sound signal form. The more the signal is divided, the more accurate the final signal is obtained, however you cant reach to the real signal ( because extreme space is needed to get the original signal ).

After quantifying the main analogue signal you can convert the decimal magnitude to the binary form.

I upload a photo for you to understand better.

And for your project, you can save your microphone data into an SD card, then read a data by using the example in Arduino site below:

https://www.arduino.cc/en/Tutorial/SimpleAudioPlayer

Best wishes

Hello,

assuming "arduino" being short for "Arduino Uno", IIRC you have a max. sampling rate of the ADC of about 10 kSPS. Might work for speech, provided you get the "trick" with equidistant sampling.

As far as I understand your basic question, you want to know how to convert the digital values back into analog voltages.

• The obvious answer would be to use a DAC (digital-to-analog-converter). Unfortunately the Arduino Uno has none on board.
• Using the PWM output pins would be another option, but the PWM frequencies are not really suitable to reproduce a speech signal.
• You could create an R-2R discrete DAC, using 6..8 pins of the Arduino (to get some minimum audio quality). This might perform reasonable well, although I'd suggest to get support from an E/E engineer to build this.

The Arduino ATmega328 16Mhz is not suitable for sound recording. It is too slow. The maximum speed of analogRead() is near 4Ksps. So maximum sound frequencie is near 2KHz. It is insufficient to speach.

But Arduino cans generate audible Low-quality sound with the help of Hardware (not Software analogWrite() ) PWM - Pulse Width Modulation.

With the help of Arduino You can only play sounds from SD-card, which were previously recorded by other sound recorder.

Sir, I want to save the binary data from serial monitor and my main problem arising is to decoding the binary data into a sound which I can play in my laptop afterwards. How is it possible, please help me?

Start with saving the data.

Then you might "wrap" this raw data into the "container envelope" of some audio format - easiest when selecting an uncompressed format (e.g.RIFF WAVE). This file should then be replayable.

About available audio formats: see wikipedia - a great resource on such information.

Or check Matlab's (provided you have access) or some other "mighty tool's" documentation: I wouldn't be surprised to see that Matlab or some Python package has support for such wrapping.

I want to save the binary data from serial monitor - There are not exist standard soft to read binary data from virtual Com-port (I suppose You use UART-USB converter for Arduino-Laptop interaction). You needs to write Yours own soft to do this. There are a lot of problems on hidh speed communication by virtual Com-port. For example, You must use block organisation of Yours data, but Arduino's RAM-size is too small for this.

I do not recomend to use Serial virtual Com-port to transfere sound data.

U. Dreher Sir, can you please elaborate the process a bit. If you are available please mail me at [email protected]; I am facing many problems doing that. Actually my target is to save any typ of data in a binary coded form and when needed then to make it in it's original form, this will save a lot of space in our hard disk.

Dear Avijit,

I think you have to define exactly the tasks what you want to implement.Then you make a functional block diagram. After that you have to define the hardware and software necessary to do that. If any function is absent or improper you will not be able to do the job. This concerns the appraoch of solving a problem. Here we only may guide your way to the solution. Give your work what it deserves from time. In this way you will get experience and proceed in your work.

Going to the problem you need a suitable digital to analog converter to be able to play your audio file. One question is what is the format and resolution of your arduino A/D converter. There are formats which you can play them directly by the PC or labtop by the aid of the sound card on the computer. Here you make full use of the D/A converter on the sound card.

This solution is hinted by Dr. Dreher.

Best wishes

Abdelhalim Zekry Sir, thanks for your valueable suggestion and making it easier to me. I will definitly follow your instructions and also Mr. Dreher sir.